The subject matter disclosed herein relates generally to detection systems and techniques, and more particularly to adjustment of output signals from radiation detectors (e.g., to correct for a non-linear response characteristic).
In certain types of imaging devices, such as positron emission tomography (PET) scanners, arrays of detector elements are used to detect radiation (511 keV annihilation photons) emitting from a radioactive tracer injected into a patient body. The annihilation photons are produced when a positron emitted from a radiopharmaceutical collides with an electron causing an annihilation event. Scintillation crystals receive the annihilation photon and generate light photons in response to the annihilation photon, with the light photons emitted to a photodetector configured to convert the light energy from the light photons to electrical energy.
Solid state photomultipliers, such as a Silicon photomultiplier (SiPM), may be used as photodetector in PET. Solid state photomultipliers provide generally high photon detection efficiency (PDE), low operating voltage (e.g., 30-100 volts), and low sensitivity to magnetic field. However, SiPMs are inherently non-linear (with respect to response at different number of light photons) when designed and operated for high overvoltage and thus high PDE.
In a PET scanner, thousands of light photons generated by a 511 keV annihilation photon in the scintillation crystals may be detected by a SiPM device in a short time duration that is comparable to the recovery time of the SiPM device. The high detection efficiency of light photons necessitates a large dynamic range when the scintillation crystals are directly coupled to the SiPM device. Otherwise, non-linearity of the SiPM device may hinder the recognition of inter-crystal events based on a summed energy, as the readout produced by a single photoelectric event in a single crystal does not equal the summed readout of multiple crystal event (e.g. Compton scatter of K X-ray escape).